Respiratory Therapy Formulas and Calculations

[Pages:10]Disclaimer:

Medicine and respiratory therapy are continuously changing practices. The author and publisher have reviewed all information in this report with resources believed to be reliable and accurate and have made every effort to provide information that is up to date with the best practices at the time of publication. Despite our best efforts we cannot disregard the possibility of human error and continual changes in best practices the author, publisher, and any other party involved in the production of this work can warrant that the information contained herein is complete or fully accurate. The author, publisher, and all other parties involved in this work disclaim all responsibility from any errors contained within this work and from the results from the use of this information. Readers are encouraged to check all information in this publication with institutional guidelines, other sources, and up to date information. Respiratory Therapy Zone is not affiliated with the NBRC?, AARC?, or any other group at the time of this publication.

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Table of Contents

Introduction .........................................................................................................................4 Formulas .................................................................................................................................5 Calculations ..........................................................................................................................11 Practice Questions ........................................................................................................73 TMC Practice Questions ............................................................................................80 Conclusion ..........................................................................................................................85 References ..........................................................................................................................86

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Introduction

Are you ready to learn about the Respiratory Therapy Formulas, Calculations, and Equations? I sure hope so because that is what this guide is all about. Inside of this book, we've created an all-in-one stop that you can use as a reference for each and every formula that you'll see as a Respiratory Therapy Student. Some are hard. Some are easy. But the good news is, I have faith that you can master them all if you set your mind to it. Practice (and lots of repetitions) makes perfect. So the more time you spend going through these formulas, the more likely it is that you'll actually learn and memorize this information. And as you'll see, we've even included some practice questions that can provide additional help as well. So if you're ready, let's go ahead and dive right in. J

Note: In general, the formulas and calculations may vary from publication to publication. With that said, we've attempted to provide the ones that will be most helpful for the Respiratory Therapy Board Exams.

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Respiratory Therapy Formulas

First and foremost, before we get into the calculations, let's first learn the formulas. These are the formulas and equations that you will be required to learn in Respiratory Therapy School.

Minute Ventilation (VE) VE = Respiratory Rate x Tidal Volume

Alveolar Minute Ventilation (VA) VA = (Tidal Volume ? Deadspace) x Respiratory Rate

Airway Resistance (Raw) Raw = (PIP ? Plateau pressure) / Flow

Mean Airway Pressure (Paw) Paw = ((Inspiratory Time x Frequency) / 60) x (PIP ? PEEP) +PEEP

Work of Breathing (WOB) WOB = Change in Pressure x Change in Volume

Alveolar-Arterial Oxygen Tension Gradient (P(A-a)O2) P(A-a)O2 = PAO2 ? PaO2

Alveolar Oxygen Tension (PAO2) PAO2 = (PB ? PH2O) x FiO2 ? (PaCO2 / 0.8)

Arterial/Alveolar Oxygen Tension (a/A) Ratio (a/A) Ratio = PaO2/PAO2

Arterial Oxygen Content (CaO2) CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x 0.003)

End-Capillary Oxygen Content (CcO2)

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CcO2 = (Hb x 1.34 x SaO2) + (PAO2 x 0.003)

Mixed Venous Oxygen Content (CvO2) CvO2 = (Hb x 1.34 x SvO2) + (PvO2 x 0.003)

Shunt Equation (QS/QT) QS/QT = (CcO2 ? CaO2) / (CcO2 ? CvO2)

Modified Shunt Equation (QS/QT) QS/QT = ((PAO2 ? PaO2) x 0.003) / ((CaO2 ? CvO2) + (PAO2 ? PaO2) x 0.003)

Arterial-Mixed Venous Oxygen Content Difference (C(a-v)O2) C(a-v)O2 = CaO2 ? CvO2

Oxygen-to-Air Entrainment Ratio (O2:Air) O2:Air = 1 : (100 ? FiO2) / (FiO2 ? 2)

Arterial Oxygen Saturation Estimation (SaO2) SaO2 = PaO2 + 30

PaO2/FiO2 Ratio (P/F Ratio) P/F Ratio = PaO2 / FiO2

Oxygenation Index (OI) OI = ((Paw x FiO2) / PaO2) x 100

Oxygen Consumption (VO2) VO2 = Cardiac Output x C(a-v)O2

Oxygen Extraction Ratio (O2ER) O2ER = (CaO2 ? CvO2) / CaO2

FiO2 Estimation for Nasal Cannula FiO2 = 20 + (4 x Liter Flow)

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Oxygen Cylinder Duration Duration = (Gauge Pressure x Tank Factor) / Liter Flow

Liquid Oxygen System Duration Duration = (344 x Liquid Weight) / Flow

Cardiac Index (CI) CI = Cardiac Output / Body Surface Area

Cardiac Output (QT) QT = Heart Rate x Stroke Volume

Cardiac Output (CO) Fick's Method CO = (O2 Consumption / CaO2 ? CvO2)

Cerebral Perfusion Pressure (CPP) CPP = Mean Arterial Pressure ? Intracranial Pressure

Mean Arterial Pressure (MAP) MAP = (Systolic BP + (2 x Diastolic BP)) / 3

Stroke Volume (SV) SV = Cardiac Output / Heart Rate

Maximum Heart Rate (HRmax) HRmax = 220 ? Age

Heart Rate on an EKG Strip (HR) HR = 300 / # of large boxes between R waves

Respiratory Quotient (RQ) RQ = VCO2 / VO2

Systemic Vascular Resistance (SVR) SVR = (MAP ? CVP) x (80 / Cardiac Output)

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Pulmonary Vascular Resistance (PVR) PVR = (MPAP ? PCWP) x (80 / Cardiac Output)

Static Compliance (Cst) Cst = Tidal Volume / (Plateau Pressure ? PEEP)

Dynamic Compliance (Cdyn) Cdyn = Tidal Volume / (Peak Pressure ? PEEP)

Deadspace to Tidal Volume Ratio (VD/VT) (VD/VT) = (PaCO2 ? PECO2) / PaCO2

Children Dosage Estimation Child Dose = (Age / Age + 12) x Adult Dose

Infant Dosage Estimation Infant Dose = (Age in Months / 150) x Adult Dose

Anion Gap Anion gap = Na+ ? (Cl- + HCO3-)

Body Surface Area (BSA) BSA = ((4 x Body Weight) + 7) / (Body Weight + 90)

Elastance Elastance = Change in Pressure / Change in Volume

Smoking Use Calculation (Pack Years) Pack Years = (Packs Smoked per Day) x (Number of Years Smoked)

Suction Catheter Size Estimation Catheter Size = (Internal Diameter / 2) x 3

Endotracheal Tube Size Estimation in Children Tube Size = (Age + 16) / 4

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